Tungsten-halogen lamps

ABSTRACT

A tungsten halogen incandescent lamp having two planar filaments which are spaced further apart at one pair of edges of the planes than at the other pair, one filament being of lower efficiency than the other filament so that in use the lamp can be orientated with the filaments further apart at the upper edges and the filament of lower efficiency uppermost whereby the temperature gradient between the top and the bottom of the filaments is reduced.

United States Patent Kenneth Buckley Robinson; Henry Alfred Fenn, bothof London, England Feb. 25, 1970 Dec. 7, 1971 Thorn Lighting LimitedLondon, England Mar. 25, 1969 Great Britain [72] Inventors App]. No.Filed Patented Assignee Priority TUNGSTEN-HALOGEN LAMPS 13 Claims, 2Drawing Figs.

U.S. C1 313/316, 313/222, 313/276 Int. Cl HOIlt 9/00 FieldofSearch313/115, 222, 223, 315, 316

{ 56] References Cited UNITED STATES PATENTS 1,483,449 2/1924 Johnson313/315 3,441,774 4/1969 Stone et a1. 313/316X Primary Examiner-RaymondF. Hossfeld Alr0rneyLaurence Burns ABSTRACT: A tungsten halogenincandescent lamp having two planar filaments which are spaced furtherapart at one pair of edges of the planes than at the other pair, onefilament being of lower efficiency than the other filament so that inuse the lamp can be orientated with the filaments further apart at theupper edges and the filament of lower efficiency uppermost whereby thetemperature gradient between the top and the bottom of the filaments isreduced.

PATENIED DEC 7197:

LEY ROBINSON KENNETH BUCK HENRY ALFRED FENN INVENTORS ATTORNEYTUNGSTEN-HALOGEN LAMPS The present invention relates to improvements intungstenhalogen incandescent lamps.

A tungsten-halogen studio lamp consisting of two parallel planarfilaments mounted in a silica envelope, has the disadvantage that thefilaments are necessarily large, which causes the size of the envelopeto be larger than the optimum size for the operating temperature of thelamp. To reduce the size of the envelope and hence its cost thedimensions of the filaments and the spacing between the filaments arereduced as much as possible. Notwithstanding these reductions, a largeenvelope is still required, and due to the risk of an explosion when alarge envelope is filled to a high pressure, the envelope is only filledto a relatively lowpressure. The filaments of the lamps thus producedare particularly prone to arcing, especially when the lamp is burnt withthe filaments at an angle of about 45 to the horizontal, which is anorientation commonly used in the studio.

It has been found that most of the arcing occurs at the top of thefilament which is uppermost in use. Normally it is the rear filamentthat is uppermost.

The arcing has been attributed to two causes. Firstly the upper filamentruns at a temperature 3050 C. higher than the lower filament, due to itsposition. Additionally there is a temperature gradient from the bottomto the top of each filament. Thus the top of the upper filament is thehottest part of the lamp and consequently the filament evaporates morerapidly there than at the rest of the filament. The tungsten halidewhich decomposes near the filament replaces tungsten on the filament butnot necessarily on the hot spots. These hot spots of the filament becomethinner more rapidly than elsewhere, their electrical resistance becomesrelatively high and hence these parts become still hotter. Theevaporation is enhanced and it has been found that a 30 C. rise in theoriginal filament-temperature causes a reduction of 25 percent in thelife of the lamp. The hotter a wire becomes the more likely it is toemit ionizing particles which may start arcmg.

Secondly in the region of the Langmuir sheath, whose dimensions arecontrolled bythe temperature and pressure of the lamp, and the viscosityand density of its fill, convection does not occur and only laminar gasflow is evident. In doublefilament tungsten-halogen studio lamps theLangmuir sheaths may overlap. Impurities such as iron in the lamp cancombine with the halogen and eventually find their way back to thefilament. They may then be flashed off as ionizedparticles. The laminarflow tends to transfer the ionized particles from the lower filament tothe top of the upper filament increasing the likelihood of arcing.

In this specification a planar filament means a filament which is largein two dimensions and relatively small in the third dimension. Thus theterm "planar filament" includes, for example, a a biplanar filament.

According to the present invention a tungsten-halogen incandescent lampcomprises two planar filaments located one in front of the other, andthe spacing between the filaments being greater at one pair of edges ofthe planes of the filaments than at the opposite pair of edges.

In a preferred form of the present invention one of the filaments is ofa lower efficiency than the other.

By using the lamp with the ends which are spaced further apart at thetop and the filament of lower efficiency uppermost the life time of thelamp can be increased and may be greater than a similar lamp of the typedescribed above.

The temperature gradient between the top and bottom of each filament isreduced and may be eliminated since there is less heat transfer betweenthe filaments at the top than at the bottom. The temperature differencebetween the front and rear filaments is reduced and in some caseseliminated by the wider spacing which gives less heat transfer and bythe lower efiiciency of the upper filament. The spacing at the top maybe made sufficient to separate the Langmuir sheaths there and theconvection between the filaments tends to prevent ionized gas beingtransferred from one filament to the other.

A embodiment of the invention will now be described with reference tothe accompanying drawings of which:

FIG. l is a front elevation of a tungsten-halogen-studio lamp; and

FIG. 2 is a side elevation of the lamp of FIG. 1.

Two tungsten filaments 11 and 12 are mounted in a silica envelope 13.The filaments are made up of substantially parallel coiled sections 14which are connected] in series and which are supported by hooks 15 fromsilica bridges l6. Metalrods 17 support the silica bridges 16. Theserods pass through a flat silica disc 18 which forms the base of theenvelope 13. Two silica tubes 19 surround the rods 17 on the side of.the disc 18 which is not enclosed by the envelope 13. The tubes 19 aresealed with pinched seals 20 and metal foils 21 are included in the sealelectrically to connect the rods M7 to terminal wires 22.

The ends 23 of the wires of the filaments are wound round the rods 17 soas to provide electrical connection between the filaments II and 12 andthe terminal wire 22.

The upper ends of the rods 17 are provided with coils 24 which arelocated in tubes 25 on the inside ofthe envelope 13.

The lamp is made by bending the rods 17 into the shape required by thespacing of the filaments and the tubes l9with the seals 20 are weldedinto the flat silica disc 18. The filaments II and 12 are mounted on therods 17 and the envelope I3 is then sealed aroundthe filaments. The fillof the envelope includes inert gas and small quantities of a halogeneither as the element or in a compound.

The filament 12 has a lower efficiency than the filament l1 and the rods17 are so bent that the filaments are further apart at the top than atthe bottom.

In normal use the filaments are 45 to the horizontal with the filamentlZabove and to the rear of the filament 11. In this way the temperaturesof the filaments are approximately the same and the tendency for arcingis less than for similar lamps with parallel filaments of equalefficiencies.

Each filament of the lamp described is a planar filament made up ofparallel coiled-wire sections connected in series. However, it ispossible to have other forms of planar filament such as, for example,one made upof a zigzagarray of coiled sections connected in series, or abiplanar filament, that is a filament in which alternate sectionsaredisplaced out of the plane of the other sections into, a second plane.Furthermore the coiled filament may be a coiled coil.

What is claimed is:

l. A tungsten-halogen incandescent lamp comprising: an, envelope; a fillof inert gas and halogen; lamp terminals; two planar tungsten filamentslocated one in front of the other inside the envelope, the spacingbetween the said filaments being greater at one pair of edges of theplanes of the filaments than at the opposite pair of edges; and lead-inconductors connecting the filaments to the terminals.

2. A lamp as claimed in claim 1 wherein one of the filaments is of lowerefficiency than the other.

3. A lamp according to claim 2 in which the filament of lower efficiencyis the rear filament.

4. A lamp according to claim I in which the filaments are made up ofparallel coiled wire sections.

5. A lamp according to claim 4 in which the sections are suspendedbetween bridge means.

6. A lamp according to claim 5 in which the bridge means are of silica.

7. A lamp according to claim 5 including hooks, the sections beingsuspended from the bridge means by the hooks.

8. A lamp according to claim 5 in which the lead-in conductors are metalrods, the bridge means being supported in the envelope by the metalrods.

9. A lamp according to claim 8 including coils and corresponding tubesthe coils being mounted at one end of each of the rods and engaging thecorresponding tubes which are provided on the inside of the envelope,the rods passing through and being-sealed in the envelope.

10. A lamp according to claim 1 in which the filaments are further apartat the edges most distant from the lamp terminals.

11. A lamp according to claim oriented during use with said edgesuppermost.

12. A lamp according to claim 2 oriented during use with the filament oflower efficiency uppermost.

13. A lamp according to claim 1 in which each filament is 5 made up offilament sections which lie substantially in the plane of the filament.

# 1C i i

1. A tungsten-halogen incandescent lamp comprising: an envelope; a fillof inert gas and halogen; lamp terminals; two planar tungsten filamentslocated one in front of the other inside the envelope, the spacingbetwEen the said filaments being greater at one pair of edges of theplanes of the filaments than at the opposite pair of edges; and lead-inconductors connecting the filaments to the terminals.
 2. A lamp asclaimed in claim 1 wherein one of the filaments is of lower efficiencythan the other.
 3. A lamp according to claim 2 in which the filament oflower efficiency is the rear filament.
 4. A lamp according to claim 1 inwhich the filaments are made up of parallel coiled wire sections.
 5. Alamp according to claim 4 in which the sections are suspended betweenbridge means.
 6. A lamp according to claim 5 in which the bridge meansare of silica.
 7. A lamp according to claim 5 including hooks, thesections being suspended from the bridge means by the hooks.
 8. A lampaccording to claim 5 in which the lead-in conductors are metal rods, thebridge means being supported in the envelope by the metal rods.
 9. Alamp according to claim 8 including coils and corresponding tubes thecoils being mounted at one end of each of the rods and engaging thecorresponding tubes which are provided on the inside of the envelope,the rods passing through and being sealed in the envelope.
 10. A lampaccording to claim 1 in which the filaments are further apart at theedges most distant from the lamp terminals.
 11. A lamp according toclaim 10 oriented during use with said edges uppermost.
 12. A lampaccording to claim 2 oriented during use with the filament of lowerefficiency uppermost.
 13. A lamp according to claim 1 in which eachfilament is made up of filament sections which lie substantially in theplane of the filament.